1. Field of the Invention
The present invention relates generally to circuit boards used in information handling systems. More specifically, the present invention provides an improved method and apparatus for improving the signal transfer characteristics of conductors, particularly differential signal conductors, used on circuit boards in information handling systems.
2. Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes, thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use, such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
As computers have increased in performance, it has become necessary to use higher data bit rates in high-density circuitry. High speed low-voltage differential signaling (LVDS) is increasingly used across multiple interfaces to provide the most efficient means for transferring data for high-speed protocols, including PCI-E, InfiniBand, SAS, FC, and SATA. LVDS uses a pair of conductors carrying signals of opposite polarity to transmit data. There are currently many buses that use LVDS to transmit data in the Gigahertz range. These buses require very fast edge rates to support the signal integrity of the digital waveforms they produce.
High speed signals require precise matching of signal pairs to avoid reflections of the signal. The connections used to transport high speed signals are generally point-to-point connections because the high speed signals cannot tolerate stubs that cause reflections and signal degradation.
In prior art circuit boards, it is not feasible to route high-speed LVDS signals to multiple locations. Most prior art circuit boards use “quick-switches” or zero-ohm resistors (jumpers) to connect signal conductors. Quick-switches pass the signals through a field-effect transistor (FET) or a series of FETs which generate RLC parasitics that degrade high-speed signals. Because of physical board routing constraints, routing the signals through zero-ohm resistors inevitably creates an impedance discontinuity, or “impedance bump” in the routing. The impedance bump creates reflections along the signal and also degrades the intrapair differential coupling ratio, thereby increasing the effects of local EMI sources on the conductor pair.
As signal routing speeds for differential signals exceed three gigabits per second (Gbps), problems with impedance mismatches and associated reflections will be exacerbated. It is apparent, therefore, that there is a need for an improved method and apparatus for connecting LVDS conductor pairs to avoid the problems associated with prior art connectors, as described hereinabove.